Smartphones have become ubiquitous. Many smartphones enable the determination of their location using geolocation systems, such as the global positioning system (GPS). Many location-based services take advantage of the capability of smartphones to determine their location to determine the location of users who have access to the smartphones. The location of users is often used by location-based services to enhance their services. For example, check-in services enable users to report their location so as to receive discounts at the location or to let their friends know where they are located.